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Metriorhynchus
Metriorhynchus is an extinct genus of marine crocodyliform that lived in the oceans during the Middle to Late Jurassic. Metriorhynchus was named by the German palaeontologist Christian von Meyer in 1830. Metriorhynchus was a carnivore that spent much, if not all, its life out at sea. No Metriorhynchus eggs or nests have been discovered, so little is known of the reptile's life cycle, unlike other large marine reptiles of the Mesozoic, such as plesiosaurs or ichthyosaurs which are known to give birth to live young out at sea. Where Metriorhynchus mated, whether on land or at sea, is currently unknown. The name Metriorhynchus means "Moderate snout", and is derived from the Greek Metrio- ("moderate") and -''rhynchos'' ("snout"). Discovery and species Fossil specimens referrable to Metriorhynchus are known from Middle-Late Jurassic deposits of England, France and Germany.Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag,116 pp. Valid species Species in this genus were traditionally classed into two skull groups: longirostrine (long, narrow jaws) and brevirostrine (short, broad jaws). However, there has been some contention as to how many of these species are valid, especially those from the Callovian. All brevirostrine species have been transferred to the genera Purranisaurus and Suchodus. *Eudes-Deslongchamps (1867–69) found there to be four Callovian species: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus.Eudes-Deslongchamps E. 1867-1869. Notes Paléontologiques. Caen and Paris: 320-392. *Andrews (1913) considered there to be seven valid species: M. superciliosus, M. moreli, M. brachyrhynchus, M. durobrivensis, M. cultridens, M. leedsi and M. laeve.Andrews CW. 1913. A descriptive catalogue of the marine reptiles of the Oxford Clay, Part Two. London: British Museum (Natural History), 206 pp. *Adams-Tresman (1987) using linear morphometrics however could only distinguish between the two skull groups, so she found there to be two species: M. superciliosus and M. brachyrhynchus.Adams-Tresman SM. 1987. The Callovian (Middle Jurassic) marine crocodile Metriorhynchus from Central England. Palaeontology 30 (1): 179-194. *Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi.Vignaud P. 1997. La morphologie dentaire des Thalattosuchia (Crocodylia, Mesosuchia). Palaeovertebrata 26: 35-59. *''M. superciliosus: Western Europe (England, France and Germany) of the Middle-Late Jurassic (Callovian and Oxfordian); ''M. moreli, M. blainvillei, and M. jaekeli are junior synonyms. *''M. hastifer: Western Europe (France) of the Late Jurassic (Kimmeridgian) *M. geoffroyii: (type species) Western Europe (England, France and Switzerland) of the Late Jurassic (Kimmeridgian); ''M. palpebrosus, and M. temporalis are junior synonyms. Two longirsotrine species, M. acutus and M. leedsi have been referred to the genus Gracilineustes.Young, Mark T., Brusatte, Stephen L., Ruta, M., Andrade, Marco B. 2009. "The evolution of Metriorhynchoidea (Mesoeucrocodylia, Thalattosuchia): an integrated approach using geometrics morphometrics, analysis of disparity and biomechanics". Zoological Journal of the Linnean Society 158: 801-859. Unnamed species Fragmentary remains attributed to Metriorhynchus are known from South America during the Bajocian Gasparini Z, Vignaud P, Chong G. 2000. The Jurassic Thalattosuchia (Crocodyliformes) of Chile: a paleobiogeographic approach. Bulletin Société Géologique de France 171 (6): 657-664 and Bathonian (both Middle Jurassic).Gasparini Z, Cichowolski M, Lazio DG. 2005. First record of Metriorhynchus (Reptilia: Crocodyliformes) in the Bathonian (Middle Jurassic) of the Eastern Pacific. Journal of Paleontology 79 (4): 801–805. However, phylogenetic analysis has shown that these species cannot be referred to Metriorhynchus.Young, Mark T., and Marco Brandalise de Andrade, 2009. "What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern, Germany." Zoological Journal of the Linnean Society, 157: 551-585. Taxonomy and phylogeny , Paris]] The genera Purranisaurus and Suchodus have been considered junior synonyms of Metriorhynchus, Recent phylogenetic analyses however, do not support the monophyly of Metriorhynchus.Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A.Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. Science 311: 70-73.Wilkinson LE, Young MT, Benton MJ. 2008. A new metriorhynchid crocodilian (Mesoeucrocodylia: Thalattosuchia) from the Kimmeridgian (Upper Jurassic) of Wiltshire, UK. Palaeontology 51 (6): 1307-1333. Some of the longirostrine forms, however, do appear to form a natural group.Mueller-Töwe IJ. 2005. Phylogenetic relationships of the Thalattosuchia. Zitteliana A45: 211–213. The cladogram presented below follows an analysis by Mark Young and Marco Brandalise de Andrade, published in November 2009. |label2=unnamed |2= }} }} }} Cladogram after Cau & Fanti (2010). }} }} }} Palaeobiology Description Averaging in length, Metriorhynchus was of a similar size to modern crocodiles. However, it had a streamlined body and a finned tail, making it a more efficient swimmer than modern crocodilian species.Massare JA. 1988. Swimming capabilities of Mesozoic marine reptiles; implications for method of predation. Paleobiology 14 (2):187-205. Salt glands Recent examination of the fossil specimens of Metriorhynchus superciliosus, have shown that adults of this species had well-developed salt glands.Gandola R, Buffetaut E, Monaghan N, Dyke G. 2006. Salt glands in the fossil crocodile Metriorhynchus. Journal of Vertebrate Paleontology 26 (4): 1009-1010. This means that like Geosaurus it would have been able to "drink" salt-water (necessary for a pelagic animal) and eat prey that have the same ionic concentration as the surrounding sea water (i.e. cephalopods) without dehydrating.Fernández M, Gasparini Z. 2008. Salt glands in the Jurassic metriorhynchid Geosaurus: implications for the evolution of osmoregulation in Mesozoic crocodyliforms. Naturwissenschaften 95: 79-84. Diet Metriorhynchus was a versatile and opportunistic predator, predating upon both the armoured ammonites and the fast moving fish; occasionally, it was also capable of capturing flying animals such as the pterosaurs and scavenging on plesiosaur and Leedsichthys carcasses on the seafloor.Forrest R. 2003. Evidence for scavenging by the marine crocodile Metriorhynchus on the carcass of a plesiosaur. Proceedings of the Geologists’ Association 114: 363-366. Palaeoecology Predators Even though Metriorhynchus was an effective predator, it was vulnerable to predation from apex predators such as Liopleurodon which could grow to 6.39 meters (21 feet) in length. Since Metriorhynchus had lost its osteoderms, "armour scutes", to become more efficient swimmers it would have had little defense against larger marine predators. See also *List of marine reptiles References Further reading *Buffetaut E. 1982. "Radiation évolutive, paléoécologie et biogéographie des Crocodiliens mésosuchienes". Mémoires Societé Geologique de France 142: 1–88 External links * Metriorhynchus fact files Category:Crocodilans Category:Marine